Free-piston gas-generators



A ril15, 1958 E. s. L. BEALE ETAL 2,830,565

FREE-PISTON GASGENERATORS Filed Jan. 29, 1954 V 3 Sheets-Sheet 1 'ApriII I5,"1'958 E. s. L. BEALE ETAL 2,

FREE-PISTON GAS-GENERATORS I Filed Jan. 29, 1954' s Sheets-Sheet 2 /N 1/5 N TORS A TTOR NE Y April 1958 E. s. L. BEALE ETAL 2,830,565

FREE-PISTON GAS-GENERATORS 3 Sheets-Sheet 3 Filed Jan. 29, 1954 m w M m M ML aw mm wd WW E 2,830,565 Patented Apr. 15, 1958 hie FREE-FIST ON GAS-GENERATORS Evelyn Stewart Lansdowne Beale, Wraysbury, and Bernard Charles Lovatt, Sunbury-on-Thames, England, assignors to Alan Muntz & Company Limited Application January 29, 1954, Serial No. 407,114

Claims priority, application Great Britain February 5, 1953 3 Claims. (Cl. 123-46) The present invention relates to free-piston, internalcombustion-operated gas-generators of the symmetrical inward-compressing type.

In gas-generators of this type two piston assemblies are driven outwards during the firing stroke of a diesel cycle and compress air in cushions. The energy thus stored in the cushions drives the piston assemblies inwards on the compression stroke of the diesel cycle thereby compressing air in compressor cylinders and delivering the compressed air into the engine-case which surrounds the deisel cylinder. The engine-case thus acts as a scavenge air receiver of substantial volume and stores the compressed air until the scavenge ports are opened on the out, or firing, stroke. The scavenge air then enters the diesel cylinder through the scavenge ports and the excess scavenge air passes out of the cylinder with the products of combustion through exhaust ports' whence the hot gases are fed to a turbine or other load.

In this type of gas-generator as normally constructed, the scavenge and exhaust ports are arranged around the diesel cylinder on either side of the plane of symmetry normal to the axis of the cylinder and passing through the centre of the combustion space, the scavenge ports being uncovered by one engine piston and the exhaust ports by the other. The exhaust ports are surrounded by an exhaust manifold which is inevitably within the engine case since the latter completely surrounds the diesel cylinder.

When running gas-generators of the type described steadily near to full load it has sometimes happened that the gas-generators have stopped for no apparent reason. An explanation of this important disadvantage has been found by observation through glass windows in the engine-case and is as follows:

When operating at or nearfull load, for example when the gas delivery pressure reaches about 50 p. s. i. g., the exhaust manifold gets very hot. Some parts of .it are red hot while other parts. are kept at a much lower temperature by contact with the water-cooled cylinder, where a joint has to be made on each side of the exhaust ports; The result of this is that parts of the external surface of the exhaust manifold are hot enough to carbonise any lubricating oil droplets which strike it, but not hot enough to burn oh the carbon as it forms. This lubricating oil comes from the compressor cylinders and is carried along with the scavenge air.

Observation through the glass windows shows that small pieces of carbon may become incandescent and break off. These pieces may be blown about by the scavenge air and fall on the partially carbonised oil or asphaltic matter, which collects on the walls of the engine-case in the course of time, and set it alight. Thus a local fire is started in the engine-case. This fire may go out or it may spread. If it spreads it is liable to do so suddenly and by burning up a large part of the oxygen in the scavenge air it may stop the engine.

As the power output from a gas-generator consists of the energy in the hot exhaust gases, they must not be cooled, for example by water-cooling the exhaust manifold. An alternative that has been tried is to apply lagging to the outside of the manifold so as to avoid any very hot surfaces in contact with the air in the enginecase. However, this has been found very difficult to do successfully, because of the wide range of temperatures, and the vibration set up by the suddent release of gas through the ports.

The present invention has for its object to provide convenient and effective means for overcoming the disadvantage described.

According to the invention, in a free-piston internalcombustion-operated gas-generator of the type specified having an engine-case surrounding the engine cylinder and acting as a reservoir for compressed air from the compressor cylinders, and having an exhaust manifold within the engine-case and surrounding exhaust ports in the engine cylinder, there is provided, within the engine-case, a compartment enclosing but spaced from the exhaust manifold, and preventing access to the outside of the manifold by air within the remainder of the engine-case. The compartment is preferably of approximately rectangular shape extending across the engine-case with its axis at right angles to the axis of the cylinders.

By means of the invention, oil from the scavenge air is prevented from reaching the surface of the exhaust manifold. Moreover, any incandescent particles from the exhaust manifold (possibly blown through the joint between the manifold and the engine cylinder) are preven ed from reaching the main parts of the engine-case.

An incidental advantage of the invention is that the heat loss from the exhaust manifold is greatly reduced, because the air in the separate compartment surrounding the manifold is stagnant, whereas the air in the enginecase is turbulent and carries away a considerable amount of heat by forced convection.

One embodiment of the invention will be described by way of example with reference to the accompanying drawings in which:

Fig. 1 is a view in elevation, with parts broken away, of a free-piston gas-generator according to the invention,

Fig. 2 is a view in sectional elevation of a part of the gas-generator of Fig. 1, to an enlarged scale, and

Fig. 3 is an enlarged sectional view on the line 33 of Fig. 2.

Referring to the drawings, the gas-generator comprises two like piston assemblies, one comprising a compressor piston 10 and a motor piston 11 rigidly connected together by a trunk 12 and the other a compressor piston 13 and a motor piston 14* connected by a trunk 15. The compressor pistons 16 and 13 operate on compressor cylinders 16 and 17 respectively and the two motor pistons in an engine cylinder 1%. The two piston assemblies are constrained to move in synchronism by means of two racks 19 and 2t? co-operating with a pinion 21 mounted upon a fixed axis 22. The racks lit and 20 having portions of circular cross-section guided in sleeves 23 and 24 as shown in Fig. 3.

In operation, air in the compressor cylinders 16 and 17 is compressed on the inward stroke of the pistons 10 and 13 and delivered to the interior of the engine-case 26 through non-return valves 50 (Fig. 2) located in head plates 27 serving to separate the compression space 25 from the inside of the engine-case 26.

The inward movement of the piston assemblies is brought about by the energy stored in the cushions 25 and 29 on the outboard sides of the compressor pistons during the previous firing stroke. When the air in the motor cylinder 18 has been compressed between the motor pistons during the inward stroke of the pistons, fuel is 3. injected through nozzles 30 and the firing stroke is initiated.

At the appropriate time during the firing stroke the piston 14 uncovers exhaust ports 32 and shortly afterwards the piston 11 uncovers scavenge ports 31 through which the air contained under pressure in the engine-case 26, as previously described, is delivered to the motor cylinder 18. The excess scavenge air together with the products of combustion passes out through the exhaust ports 32 into an exhaust manifold 33 and thence to a receiver 34. Air is drawn into the spaces 25 (Fig. 2) of the compression cylinders through non-return suction valves 35.

As can be seen from Figs. 2 and 3, the exhaust manifold 33 is enclosed within a compartment formed as an approximately rectangular tunnel whose four walls 36, 37, 38 and 39 extend from the top to the bottom of the engine-case 26, the diesel cylinder 18 passing transversely through this tunnel. The tunnel extends sufliciently in the direction of the axis of the cylinders to enclose the exhaust manifold 33.

The four walls 3639 of the compartment form part of the structure of the engine-case 26 which is either a casting or fabricated from heavy gauge steel plate and the compartment enclosed by the walls 3639 is made gas-tight to the outside air. In the example illustrated this is done by welding the lower ends of all four walls to the engine-case, or by casting these walls solid with the engine-case, and by providing the upper ends of the walls with aflange 40 over which is bolted a flange 41 welded to the exhaust branch 45. An exhaust pipe 42 connected to the receiver 34 has a flange 43 which is bolted to the fian ges 40 and 41.

The lower end of the compartment 36-39 is closed by a cover plate.

It is not necessary that the joints between the exhaust manifold 33 and the cylinder 18 should be gas-tight, as the pressure in the compartment reaches a steady value intermediate between the exhaust gas pressure and the engine-case pressure which is always slightly higher. Joints such as are shown in Fig. 2, permitting some relative movement between the exhaust manifold and the cylinder wall to allow for diflerential expansion, are suitable.

Fairly well-fitting joints are provided between the walls of the compartment and the diesel cylinder 18. The diesel cylinder 18 is assembled in the engine-case 26 by insertion from the left in Fig. 2. The inboard Wall 38, that is the wall nearer the centre of the engine, engages a seating 44 on the diesel cylinder. The outboard Wall 39 is provided with a hole and the annular space is closed by an annular plate 46 bolted to the outboard wall 39 and is sealed by a suitable packing ring 52 to the outside of the diesel cylinder. This construction enables the packing ring 52 to be renewed without the need to remove the diesel cylinder.

By constructing the compartment enclosing the exhaust manifold in the manner described, so that it extends across the whole diameter of the engine-case, it is possible, without modification of the basic structure of the engine-case, to arrange that the exhaust is taken out from the manifold in either an upward or a downward direction, as may be required. The exhaust branch 45 is shown stiffened by members 47.

We claim:

1. A free-piston internal-combustion-operated gas-generator comprising an engine cylinder, two engine pistons in said cylinder, two compressor cylinders arranged on the out-board sides of said engine cylinder, a compressor piston in each of said compressor cylinders operatively connected with one of said engine pistons, an engine-case surrounding said engine cylinder and acting as a reservoir for compressed air from said compressor cylinders, exhaust ports in said engine cylinder, an annular exhaust manifold within said engine case surrounding said exhaust ports, and a compartment within said engine case separating the entire outer surface of said manifold from the engine case and providing an enclosed substantially stagnant-gas-filled space surrounding said manifold.

2. A gas-generator according to claim 1, wherein said compartment is of approximately rectangular shape.

3. A gas-generator according to claim 1, wherein said compartment extends across said engine case with its axis at right angles to the axis of said cylinders.

References Cited in the file of this patent UNITED STATES PATENTS 2,406,037 Ramsey Aug. 20, 1946 2,408,089 Muntz Sept. 24, 1946 FOREIGN PATENTS 230,781 Switzerland Apr. 17, 1944 

